Si-O Bonds Research Articles

Stress Relaxation in SGOI Structure Obtained by Condensation

The development of effective buffer layer has required years of work in order to obtain relaxed SiGe substrates [1]. However, main drawback of this approach relies on the presence of embedded and numerous dislocations which can be detrimental for optimal applications. Recently, a surprising relaxation phenomenon has been observed on specific Silicon-Germanium On Insulator (SGOI) structures [4-5].It has been observed that when the sample is heated, slippage is observed at the SGOI/Buried Oxide (BOX) interface.The phenomenon is not clearly understood. However, several explanations have been raised. It can be explained by the mechanical properties by Ge-O bonds which are weaker than the Si-O bonds at the SGOI/BOX interface causing the slip. [2] Also, the Ge atoms in the last crystalline layer at the BOX interface decreases the quantity of Si atoms inducing less bonds between the Si atoms of SGOI and the BOX.We suggest to take advantage of this phenomenon to obtain fully relaxed SGOI layers without dislocations. This new approach would allow to create high performance relaxed SGOI layers in industrial conditions with 300 mm wafers. This innovation is relevant for several applications, such as optical applications and the formation of base substrate to generate tensile Si epitaxy layer. It has to be noticed that any Ge concentration until pure GeOI structure is possible.Figure 1 shows the different process steps to obtain relaxed SGOI layer explained below. SiGe epitaxy (fig.1-a) is performed on an 300mm SOI wafer by Rapid Thermal Chemical Vapor Deposition (RT-CVD). Germane (GeH4) and Dichlorosilane (DCS) are used as precursor gases to obtain a 20nm thick fully strained Si0.8Ge0.2 layer. Upstream work is performed to improve the uniformity of the SiGe layer (thickness and composition) within the 300mm wafer. Indeed, they are key parameters impacting Ge concentration within wafer uniformity obtained after condensation.[3]Then, condensation is performed (fig.1-b) using thermal oxidation in a 300mm industrial furnace under N2/O2 atmosphere at 1000°C during several hours. Condensation is tuned to obtain the desired Ge concentration in the SGOI structure. Condensation allows to transform a SiGe/Si/BOX structure into SiGe/BOX structure called SGOI. Two mechanisms are involved in the condensation. The first mechanism is the Si-selective oxidation in the SiGe layer allowing Ge atoms to accumulate at the oxidation interface. The second mechanism is the Ge diffusion in the structure which allows SiGe inter-diffusion. The Ge atoms are maintained and homogenized in depth of the SGOI layer during the interdiffusion mechanism thanks to the BOX acting as a diffusion barrier. [2]During this work, the layer composition, the thickness as well as the stress were characterized by ellipsometry, XRR, XRD and SIMS. In addition, the surface was analyzed by AFM to detect any crystal defects.In this study, we propose to investigate the relaxation of SGOI layer with a concentration of Ge=50% because such structure shows no defects after condensation [2]. Thereafter, it will be possible to carry out GeOI in the future.Figure 2 shows SiGe thickness and density measurement by XRR. A thickness variation of 13.67 A and a density variation of 0.22g/cm3 of the SGOI layer after condensation on the whole wafer is obtained. The average density is 4,31g/cm3 with a concentration of %Ge=51% which was our target concentration.Then, the relaxation phenomenon is studied using anneals in the temperature range [700;900] °C during several hours. Indeed, we chose a temperature close to the SiO2 viscosity temperature and a long annealing time allowing to generate a slow slip thus limiting defects.Figure 3 shows a RSM map obtained by XRD of an Si0.5Ge0.5OI layer after annealing at 800°C for 2h. The mapping shows Si substrate as well as the layer relaxed along the (113) and (224) planes at an angle Φ=45°. RSM map allows to calculate the relaxation rate which is 22%. The relaxation on the sample is a success that remains to be improved by annealing time or temperatures to be optimized.This new approach would allow the realization a defect free relaxed SGOI layer under industrial conditions on a 300mm wafer. It would provide a new method for applications such as optical or the growth of tensile Si channels.[1] P.M.Mooney, Materials Science and Engineering, 1996[2] F.Roze. PhD thesis, 2018[3] D.Valenducq, PhD thesis, 2021[4] V.Boureau et al., ECS, 2018[5] Usuda, Koji, et al., Solid-State Electronics, 2013 Figure 1

Direct non-oxidative methane coupling on vitreous silica supported iron catalysts

Direct non-oxidative methane coupling (NMC) is one of the promising pathways for methane upgrading into value-added olefin and aromatic hydrocarbons. The silica-supported iron (i.e., Fe/SiO2) catalyst has been reported effective for NMC, but the effects of silica support on the catalyst property and NMC performance have rarely been explored. In this work, we prepared a vitreous silica-supported iron (Fe/SiO2-V) catalyst by flame fusion of a mixture of quartz silica and fayalite. The physicochemical properties and NMC performance of the as-prepared catalysts were measured. Compared to crystalline cristobalite support in Fe/SiO2 catalyst that has been studied previously, vitreous silica support has disordered Si-O bonds and structural defects, enabling better iron dispersion and more vital metal-support interaction. The as-prepared Fe/SiO2-V catalyst had a shorter induction period in methane activation and lower coke yield in NMC. The increase in iron concentration in Fe/SiO2-V catalysts elongated the catalyst induction period and promoted aromatics and coke formation. The coke type of the spent Fe/SiO2-V catalyst is more uniform than the cristobalite-supported iron catalyst.

Ceramic precursor-phthalonitrile hybrid with improved high heat resistance through constructing binary continuous phases

Achieving organic–inorganic hybrids with improved heat resistance above 500 °C using inorganic materials as filler remains a challenge because inorganic constitutes could not form continuous inorganic phases in hybrids. Here, we obtained organic–inorganic phthalonitrile hybrids with increased heat resistance using ceramic precursor (SiBCN) as the inorganic source. The results showed that hybrids formed Si-O bond between phthalonitrile and the ceramic precursors. The carbon fiber reinforced composites of hybrids exhibited high glass transition temperatures (over 700 °C). The hybrid with 30 wt% SiBCN displayed a high temperature for losing 10 % weight (above 555.4 °C (N2)), and high mass residue (over 75 % at 900 °C (N2)). The improved heat resistance of the hybrid was originated from the continuous inorganic phases derived from the ceramic precursors delaying transfer and escape for the small molecules generated in the phthalonitrile resin at elevated temperature. Furthermore, the hybrid showed excellent high-temperature stability of thermal conductivity. The as prepared organic–inorganic hybrids could potentially replace ceramic-based materials in servicing temperatures ranging from 500−700 °C.

Atomistic insight into the ferroelastic post-stishovite transition by high-pressure single-crystal X-ray diffraction

Abstract The post-stishovite transition is a classic pseudo-proper typed ferroelastic transition with a symmetry-breaking spontaneous strain. This transition has been studied using high-pressure spontaneous strains, optic modes, and elastic moduli (Cij) based on the Landau modeling, but its atomistic information and structural distortion remain poorly understood. Here we have conducted synchrotron single-crystal X-ray diffraction measurements on stishovite crystals up to 75.3 GPa in a diamond-anvil cell. Analysis of the data reveals atomic positions, bond lengths, bond angles, and variations of SiO6 octahedra across the transition at high pressure. Our results show that the O coordinates split at ~51.4 GPa, where the apical and equatorial Si-O bond lengths cross over, the SiO6 octahedral distortion vanishes, and the SiO6 octahedra start to rotate about the c axis. Moreover, distortion mode analysis shows that an in-plane stretching distortion (GM1+ mode) occurs in the stishovite structure at high pressure while a rotational distortion (GM2+ mode) becomes dominant in the post-stishovite structure. These results are used to correlate with elastic moduli and Landau parameters (symmetry-breaking strain e1–e2 and order parameter Q) to provide atomistic insight into the ferroelastic transition. When the bond lengths of two Si-O bonds are equal due to the contribution from the GM1+ stretching mode, C11 converges with C12, and the shear wave VS1[110] polarizing along [110] and propagating along [110] vanishes. Values of e1–e2 and Q are proportional to the SiO6 rotation angle from the occurrence of the GM1+ rotational mode in the post-stishovite structure. Our results on the pseudo-proper type transition are also compared with that for the proper type in albite and improper type in CaSiO3 perovskite. The symmetry-breaking strain, in all these types of transitions, arises as the primary effect from the structural angle (such as SiO6 rotation or lattice constant angle) and its relevant distortion mode in the low-symmetry ferroelastic phase.

Tribological properties of Ni-BP/Ni coatings produced by electroless co-deposition

In the field of tribology, black phosphorus (BP) with a layered structure has displayed outstanding performance. To alleviate the high friction and corrosive wear of the friction pairs of marine equipment, four types of coatings including Ni-PP, Ni-BP/Ni30, Ni-BP/Ni60, and Ni-BP/Ni90, which were labelled with different deposition time, were prepared on Q235 steel via electroless co-deposition technique. A ball-on-disk reciprocating tribometer was used to evaluate their tribological properties in 3.5 wt% NaCl, poly-α-olefin 6 (PAO6), and deionized water, respectively. The results show that the Ni-BP/Ni coatings sliding in 3.5 wt% NaCl exhibited better friction reduction and wear resistance than that in deionized water. The Ni-BP/Ni30 coating sliding in 3.5 wt% NaCl showed excellent tribological properties and compared with the Ni-P coating, its average friction coefficient was reduced by 40 % at a load of 4 N and the wear scar cross-sectional area was reduced by 77 % at a load of 10 N. The enhanced tribological properties were attributed to the lamellar slip of BP nanosheets and the formation of a tribofilm composed of NiO, Ni(OH)2, and SiO bonds and an adsorbed film with BP nanosheets. The Ni-BP/Ni coatings present a promising application in seawater corrosive environment.

Ultrasonic studies of alkali-rich hydrous silicate glasses: Elasticity, density, and implications for water dissolution mechanisms

AbstractThe acoustic velocities of three series of alkali-rich hydrous silicate glasses were determined at ambient conditions using ultrasonic interferometry. The sound velocities and calculated elastic properties are nearly linear functions of dissolved water content. The water content derivatives of both compressional [d(VP)/d(XH2O)] and shear wave velocity [d(VS)/d(XH2O)] decrease with increasing Na2O content, which suggests that increasing sodium content might weaken the effect of water on acoustic velocities. For each glass series, the shear modulus decreases with increasing water content, whereas the adiabatic bulk modulus (KS) varies little with water content. By comparing our results of KS to previously published data on hydrous alkalic (rhyolite, phonolite, and trachyte) glasses, we speculate that H2O may have a negligible effect on the compressibility of alkalic glasses/melts. The measured densities of each series of glasses were converted to molar volumes and extrapolated to the hypothetical pure water component to derive the partial molar volume of water (VH2O). The resulting VH2O at room pressure and temperature was found to be independent of composition for the three series of glasses, with a value of 10.4 ± 0.5 cm3/mol, whereas the partial molar bulk modulus (KS) of water is composition-dependent, suggesting that VH2O may depend on composition at elevated pressures. Furthermore, the Poisson’s ratio (ν) increases linearly with increasing water content for all three composition series. Therefore, the similar behavior of Al-free and Al-bearing glasses implies that water depolymerizes melts in both systems. The decrease of water content derivative of the Poisson’s ratio [d(ν)/d(XH2O)] with increasing Al/(Al+Si) indicates that water interaction with Al-O bonds to produce Al-OH depolymerizes peralkaline silicate melts less effectively than with Si-O bonds to form Si-OH. Hence, we speculate that water prefers to interact with Si-O bonds rather than Al-O bonds in peralkaline silicate systems. The dissolution mechanisms of water between peraluminous and peralkaline melts might be different, which merits further research.

Synthesis of SiC films by Atmospheric Pressure Chemical Vapor Deposition using Dimethylisopropylsilane Polymeric Precursor

Abstract: Silicon carbide (SiC) thin films were deposited on Quartz, SiC, and GaAs substrates under a hydrogen (H2) ambient at 850°C using dimethylisopropylsilane [CH(CH3)2SiH(CH3)2] as a single molecular polymeric precursor by the atmospheric pressure chemical vapor deposition (APCVD) technique. Effects on the SiC films from variation of precursor to H2 flow ratio in the reactive chamber as well as those which resulted when vacuum or positive pressures are utilized during temperature ramping have been investigated. Detailed analysis of Fourier Transform Infrared Spectroscopy (FTIR) results indicate the formation of SiC at 850°C in accordance with residual Si-CH2, Si-CH3 and Si-O bonds. Confirmed by either X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) or Energy Dispersive Spectroscopy (EDS), results show that the produced SiC films are dense, rough surfaced, void-free, and consist of a crystalline core showing the presence of beta-SiC and small amounts of alphaSiC. Pre-experimental thermodynamic modeling provided the valuable insight that an increase of the precursor to direct H2 flow ratio would provide a decrease of unreacted carbon in the SiC matrix yielding higher quality SiC films. These simulations also have shown reasonable agreement with our experimental observations. Keywords: SiC thin Film, Polymeric Precursor, Chemical Vapor Deposition, Thermodynamic Modelling

The loading speed facilitating stress relaxation behaviors of surface-modified silicon: a molecular dynamics study.

Time-dependent plastic deformation commonly exists in silicon-based microelectronic contact. The stress relaxation behaviors of SiO2/Si bilayer composite are studied using molecular dynamics simulation by varying loading speed. The results imply that the indentation force decreases sharply at the initial and linearly towards the end of holding, and the amount of stress relaxation increases with the increasing loading speed. The plastic deformation of confined amorphous SiO2 film is carefully analyzed based on the amorphous plasticity theories; variations of coordinated silicon atoms and Si-O bond number indicate that the films are further densified at different degrees depending upon loading speed during holding. The densification is strengthened at a higher speed because much more activated shear transformation zones (STZs) and accumulated free volume generate within films indented at higher speed. The phase transformation of monocrystalline silicon is observed in indented silicon during holding; the Si-II and bct-5 silicon atoms increase with time and loading speed.

Hydration Mechanisms of Alkali-Activated Cementitious Materials with Ternary Solid Waste Composition.

Considering the recent eco-friendly and efficient utilization of three kinds of solid waste, including calcium silicate slag (CSS), fly ash (FA), and blast-furnace slag (BFS), alkali-activated cementitious composite materials using these three waste products were prepared with varying content of sodium silicate solution. The hydration mechanisms of the cementitious materials were analyzed by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. The results show that the composite is a binary cementitious system composed of C(N)-A-S-H and C-S-H. Si and Al minerals in FA and BFS are depolymerized to form the Q0 structure of SiO4 and AlO4. Meanwhile, β-dicalcium silicate in CSS hydrates to form C-S-H and Ca(OH)2. Part of Ca(OH)2 reacts with the Q0 structure of AlO4 and SiO4 to produce lawsonite and wairakite with a low polymerization degree of the Si-O and Al-O bonds. With the participation of Na+, part of Ca(OH)2 reacts with the Q0 structure of AlO4 and the Q3 structure of SiO4, which comes from the sodium silicate solution. When the sodium silicate content is 9.2%, the macro properties of the composites effectively reach saturation. The compressive strength for composites with 9.2% sodium silicate was 23.7 and 35.9 MPa after curing for 7 and 28 days, respectively.

Spatial distribution and benthic risk assessment of cyclic, linear, and modified methylsiloxanes in sediments from Tokyo Bay catchment basin, Japan: Si-based mass profiles in extractable organosilicon

We investigated the spatial distribution, mass profiles, and benthic risk assessment of a wide range of methylsiloxanes (MSs), including 7 cyclic MSs (CMSs; D3–D9; the number refers to the number of SiO bonds), 13 linear MSs (LMSs; L3–L15), and 15 modified and other MSs (MMSs) in sediments from the Tokyo Bay catchment basin, Japan. We observed widespread distribution of MSs (ΣCMS, ΣLMS, and ΣMMS) in the sediment samples, with concentrations of 1.0–6180 ng/g dry weight (dw), 1.8–10,100 ng/g dw, and < 0.31–210 ng/g dw, respectively. Our study is the first to measure various MMSs modified with hydrogen, vinyl, or phenyl groups; however, only methyltris(trimethylsiloxy)silane and phenyltris(trimethylsiloxy)silane were detected with high occurrence frequency. Notably, no elevated concentrations of MSs were observed downstream of silicone manufacturers, whereas the sediment was characterized by a specific D4/D5 ratio. With the Si-based mass profiles in extractable organosilicon (EOSi), the measured CMSs, LMSs, and MMSs accounted for 5.4%, 7.8%, and 0.2%, respectively. Unidentified EOSi (unknown fraction) constituted a major proportion of the EOSi in the sediment, with a mean of 87%, suggesting that the organosilicon environmental emissions were more than the measured MSs. In risk assessment of the adverse effects of D4, D5, and D6 in sediment on benthic organisms, the respective distributions indicated no overlap between the 95th percentile field sediment concentration and the 5th percentile chronic sediment no-effect concentration in organic carbon-normalized concentration. Although the hazard quotient compared with the predicted no-effect concentration for D5 and D6 exceeded the threshold level (hazard quotient ≥1), the results of probabilistic risk assessment for the three CMSs were not high enough to indicate a threat to benthic organisms in the study area.

Chemical weathering mechanism of Albite-rich rocks in Grottoes under an acidic environment: An atomistic view from ReaxFF simulation

This current ReaxFF simulation provides atomic-level monitoring of the reaction details as well as dynamics of Albite under acidic solution over a nanosecond time scale. 30% H-O bond dissociation in 10% H2SO4 solution and ∼ 0.9% Si-O/Al-O bonds breakage in Albite during 20 ps was evaluated according to the time evolution of number of H-O bonds, Si-O and Al-O bonds at a higher temperature of 323 K. The breakage of Si-O/Al-O bonds within the tetrahedron configuration makes Na atoms be less restricted within the network and generates open channel for Na migration, resulting in further diffusion to the Albite-water interface and complete release into the aqueous medium. A consecutive dissociation of H2SO4 can further accelerate the formation of SO42- products as the H dissociate from H2SO4 molecules. The migrated Na cations tend to combine with SO42- and form Na-SO4 ions pair, leading to a complicated zigzag motion in 3D space and a migration trend towards the aqueous medium along Z-axis direction and a sharp peak at 2.3 Å in Na-O pair RDF.

Enhancing Reliability and 2 mm-Axial Mechanical Bending Endurance by Gate Insulator Improvements in Flexible Polycrystalline Silicon TFTs

In this study, the electrical performance and bending stress endurance of flexible low-temperature polycrystalline silicon thin film transistors (LTPS TFTs) are enhanced by increasing the helium concentration (1500 sccm) during gate insulator (GI) manufacture to create a high-quality GI device. Experimental results confirm that the subthreshold swing (S.S.) and mobility of these new &#x201C;high-flow&#x201D; devices are better than those with a lower helium concentration, which we term &#x201C;low-flow&#x201D; devices. The flow of helium gas is increased to achieve a better-quality oxide layer. The energy-dispersive X-ray spectroscopy (EDS) line data show a clear enhancement in oxygen content in the devices under this helium gas process. After mechanical compression and tensile bending stresses of 100000 iterations in the channel width-axis direction, perpendicular to the channel, with bending at <inline-formula> <tex-math notation="LaTeX">${R} = {2}$ </tex-math></inline-formula> mm, the modified GI devices with their more Si-O bond content exhibit less stress damage in the GI layer than do low-flow devices. As a result, this new manufacturing condition can effectively reduce the electrical degradation after negative-bias temperature stress (NBTS), and improve the overall electrical performance.

Effects of processing temperature on the corrosion and tribocorrosion resistance of perhydropolysilazane-derived coatings on AISI 304 steel

Ensuring a highly corrosion and erosion resistant surface is critical to the reliability and structural integrity of steel canisters for long-term nuclear waste storage in corrosive environments. In this work, perhydropolysilazane (PHPS)-derived coating has been successfully applied to enhance the pitting and tribocorrosion resistance of 304 stainless steels in 0.6 M NaCl solution. Two types of coatings were synthesized on the stainless steel substrate by crosslinking PHPS at room temperature or 600 °C, resulting in different mechanical and corrosion performance. Raman spectra revealed that SiO bonds were generated in the coating crosslinked at room temperature after corrosion, while absent in that pyrolyzed at 600 °C. In tribocorrosion tests, both coatings were protective to the steel substrate, with the protective effect being more pronounced in the 600 °C pyrolyzed coating. Overall, the PHPS-derived coating synthesized at 600 °C exhibited better protection for steel in wear and corrosion coexisting environments than those synthesized at room temperature.

Thermal Migration Behavior of Na+, Cu2+ and Li+ in Montmorillonite

The main aim of this paper is to study the cation fixation sites in montmorillonite after heating at different temperatures. Montmorillonite was used to adsorb cations (Na+, Cu2+ and Li+) in the solution, and the montmorillonite-adsorbed cations were heated at different temperatures (unheated, 100 °C, 200 °C and 300 °C) for 25 h. Subsequently, the basal spacing of montmorillonite treated at different temperatures was monitored by X-ray diffraction (XRD). The exchangeable cationic content (Na+, Cu2+ and Li+) in montmorillonite was determined based on an inductively coupled plasma emission spectrometer (ICP-OES). In addition, the stretching and bending vibration changes in the OH group and the Si-O bond in montmorillonite were detected by Fourier transform infrared spectroscopy (FTIR). The vibration changes were related to the cation fixation sites. The XRD data showed that when the heating temperature reached 200 °C, the structure of montmorillonite adsorbing Li+ and Cu2+ ions completely collapsed, but the layer spacing of montmorillonite adsorbing Na+ decreased slightly, which indicated that Li+ and Cu2+ were more easily able to enter the crystal structure. The ICP-OES results showed that the contents of exchangeable Na+, Cu2+ and Li+ in montmorillonite decreased with the increase in heating temperature, and Li+ was more easily fixed by montmorillonite than Na+ and Cu2+. The FTIR data showed that when montmorillonite adsorbed with Li+ was heated at more than 200 °C, a new OH stretching vibration band appeared at 3971 cm−1, which may be caused by the migration of Li+ into the octahedral vacancy to form a local trioctahedral structure. Na+ has a large radius; it can only be fixed near the OH group and may not enter the tetrahedron/octahedron of montmorillonite. The number of charges carried by Cu2+ is high and the dehydration enthalpy of hydrated Cu2+ is high. When the heating temperature was greater than 200 °C, Cu2+ mainly entered the hexagonal cavity of the tetrahedron and caused slight changes in the OH bending vibration. The vibration of the Si-O bond hardly changed after montmorillonite adsorbed Na+, but the stretching vibration peak of the Si-O bond moved to the high value region after adsorbing Cu2+ and Li+, which was speculated to be related to the migration of Cu2+ and Li+ into the crystal structure.

Hydrophobic agents and pH modification as comparative chemical effect on the hydrophobic and photocatalytic properties in SiO2-TiO2 coating

The SiO2-TiO2 composite has been studied through several techniques obtaining different morphologies and specific properties of SiO2 and TiO2. Nevertheless, the modification of the synthesis pH and the addition of different hydrophobic agents, such as hexamethyldisilazane (HDMS) and polydimethylsiloxane (PDMS), have not been thoroughly studied and reported. This work assessed the presence of two different hydrophobic agents and the pH modification. The SiO2-TiO2 coating was synthesized through two vias, basic and acid environment, employing the sol–gel method coupled to the sonochemistry technique. Moreover, the change of pH and use of P25 TiO2 nanoparticles and TiO2-synthesized nanoparticles allows establishing a relationship with the self-cleaning properties. The samples of SiO2-TiO2 composite were analyzed by AFM, indicating a variation in surface morphology and roughness concerning the PDMS and HMDS hydrophobic agent. ATR-FTIR analysis exhibit changes in intensity in vibrations of the Si-O, PDMS, and HMDS bonds. Raman spectroscopy results show the vibrations of the anatase and rutile phases of the TiO2 and the corresponding vibrations to the hydrophobic agents. The evaluation of self-cleaning properties demonstrated changes from the hydrophobic state to the hydrophilic state due to the addition of the nanoparticles of TiO2 to the SiO2. The photocatalytic activity was modified and improved in the HMDS-1 coating due to the hydrophobic agent and type of nanoparticles. To compare the effect of the pH in the PDMS and HMDS coatings, carried out with cyclic voltammograms and Differential Capacitance spectra. Finally, the storage time of SiO2-TiO2 coating was improved using the HMDS hydrophobic agent.

Two-photon absorption induced dangling bonds in amorphous silica revealed by molecular dynamics simulations

The amorphous silica (a-silica) has been troubled by dangling bonds induced strong optical absorption of intense ultraviolet (UV) rays, where the two-photon absorption (TPA) plays a critical role in the formation of dangling bonds. Through the combination of Keldysh theory and molecular dynamics, we studied the effects of TPA on the evolution of dangling bonds in a-silica, where the ab initial calculations need a larger size of amorphous structure. The damage precursor of (Si-O)3 rings experimentally observed was reproduced, a process where the strained Si-O bonds acted as the TPA site. We showed that TPA played a critical role in initiating dangling bonds and the following densification process depressed it. Formation channels for oxygen deficiency center I (ODC(I)) and ODC(II) were shown, as well as the interconversion with Frenkel-type defects. Our research describes the static and dynamic properties of dangling bonds and gives an interpretation of experimental observations.

Nanosilica from Rice Husk Synthesized by a Simple Heating Method and its Characterization

Nanosilica from rice husk ash (RHA) has been synthesized by a simple heating method. The obtained nanosilica was characterized by several techniques such as x-ray diffractometer (XRD), Fourirer transform infrared (FTIR), scanning electron microscope (SEM), and simultaneous thermal analysis (STA). The products had white color indicating that there were no impurities such as carbon or other elements. The XRD showed that the obtained nanosilica exhibited the pattern of amorphous silica material. FTIR spectra confirmed Si-O-Si and Si-O bonds in the obtained nanosilica. SEM images displayed the agglomeration of nanosilica particles with the average diameter of about 12 nm. STA showed that acid treatment was needed to remove carbon or mettalic ellements from nanosilica during the heating process. These results were important in supporting the utilization of rice husk to convert into other more valuable products with a simple method.

A DFT-Based Descriptor to Predict the Water Vapor Corrosion Resistance of Rare-Earth Monosilicates.

Rare-earth monosilicates are used as environmental barrier coatings (EBCs) due to their excellent water vapor corrosion resistance. However, existing experimental studies on the water vapor corrosion behavior of rare-earth monosilicates are discrepant and even contradictory. Previous theoretical investigations on water vapor corrosion resistance mainly focus on a Mulliken analysis of Si-O bonds in the monosilicates. In this study, the structural and electronic properties of rare-earth monosilicates have been studied by density functional theory (DFT) calculations, and a descriptor correlated to the corrosion resistance has been developed. The maximum isosurface value of the valence band maximum (VBMFmax) can be used to predict the water vapor corrosion resistance of RE2SiO5. The results show that RE2SiO5 with a smaller VBMFmax may have better water vapor corrosion resistance.

Epidote as a conveyor of water into the Earth’s deep mantle in subduction zones: Insights from coupled high-pressure and high-temperature experiments

Abstract Epidote is a major hydrous mineral in subducted mafic oceanic crust. Understanding its stability in the subduction zone environment is important for evaluating its role as a conveyor of water into the deep Earth. Here we report experimental results on epidote by simulating the high-pressure-temperature (P-T) conditions of the plate subduction environment. We used a diamond-anvil cell with an external resistance heating system, combined with in situ X-ray diffraction (XRD) and Raman spectroscopy techniques. Experiments at ambient pressure and high temperatures indicate that epidote starts to decompose at 1223 K and breaks down completely at 1373 K. In situ XRD analyses show no phase transition at temperatures up to 1272 K and pressures up to 14.0 GPa. Raman spectra indicate that epidote is stable at 1272 K and 14.0 GPa, but the energies of two Si-O bonds (ν2,ν5) and one M-O bond (ν3) increase with increasing temperature. The cation H+ moves for a distance when the P-T is increased to 13.0 GPa and 1123 K. Based on the thermal structure of subducted slabs in typical hot and cold subduction zones, we infer that epidote can convey water downward into the mantle transition zone through subducted mafic oceanic crust.

Preparation sodium silicate from rice husk to synthesize silica nanoparticles by sol-gel method for adsorption water in analysis of methamphetamine

Numerous uses of silica nanoparticles include medication delivery, lightweight aggregates, and energy storage. This work synthesized SiO2NPs from rice husk (RH) by a sol-gel extraction method. Fourier transform infrared (FTIR), Raman spectroscopy, X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM) with energy-dispersive X-ray (EDS) were used to analyze the extracted SiO2NPs. XRD diffraction indicates SiO2NPs, and the Debye Scherrer particle size equation shows that the particle size ranges between 43 and 97 nm. SEM image shows the structure of produced exhibits an agglomeration propensity. XRF results confirm that Si and EDS results confirm that Si and O. FTIR and Raman spectra show Si-O-Si and Si-O bonds. The adsorption of methamphetamine consistent with the Langmuir isotherm with a maximum adsorption capacity of 333.3 mg/g. The kinetic adsorption of methamphetamine consistent with the pseudo-second-order kinetic.